The present invention relates to an apparatus for the conversion of polymer waste, whether in solid and/or liquid form, herein interchangeably described as hydrocarbonaceous material, polymer waste and/or polymeric material, to condensable, non-condensable and solid hydrocarbon products. Condensable hydrocarbon products include synthetic petroleum and a variety of its fractions including but not limited to light sweet crude oil, fuel additives, base oil, slack wax, paraffin wax, microcrystalline wax and condensate dominated by aromatic petroleum hydrocarbons. The non-condensable hydrocarbon product is a gas. The solid hydrocarbon product is a finely divided carbon char. In particular, the present invention is a continuous, zone-delineated pyrolysis apparatus, having capability to simultaneously produce multiple products, one of which, a hard wax, is produced from the apparatus at temperatures lower than typical pyrolysis conversion temperatures.
Converting waste polymers to obtain useful end products via pyrolysis has been a goal sought by many, for many years. Prior art involving pyrolytic decomposition of polymers largely relies on batch, semi-batch or serial batch processes limited in commercially viable application by their operating complexity and inability to continuously process mixed, poorly sorted and/or contaminated polymer waste without fouling. Many claim that serial batch processes comprised of a series of batch reactors progressively operated in a set sequence are “continuous” merely because some product is constantly being discharged from one or more exit ports connected to the batch reactors by a manifold or other suitable exit configuration. Polymer conversion processes include the primary processes of chemical depolymerization, gasification with partial oxidation, and thermal cracking, including pyrolysis, either with or without catalytic cracking and reforming, as well as the secondary process of hydrogenation. Chemical depolymerization has mainly been limited to decomposition of polyesters e.g. PET, and polyurethanes, with secondary application to polyamides, polycarbonates and polyacetals. This method is generally restricted to decomposition of condensation polymers, targeting monomer yield.
Gasification and partial oxidation of waste polymers typically targets production of mixtures of carbon monoxide and hydrogen generally known as syngas. Although partial oxidation can be a more efficient process than steam methane reformation in terms of reactor size and process rate, partial oxidation produces a lower comparative hydrogen yield. Little, if any, condensable hydrocarbons are produced.
Thermal cracking processes employ thermal decomposition resulting in complex mixtures. Reaction temperature, coupled with molecular retention times within respective desired temperature ranges, is the most significant reaction variable, influencing both polymer conversion and molecular distribution of conversion products. Accordingly, efficient control of reaction temperature and residence times is paramount in importance to maximize yield of the desired product mix. Batch, semi-batch and serial batch processes experience difficulty in efficiently achieving and maintaining control of reaction temperatures and residence times due to problems resulting from, among other things, inefficient heat transfer through the waste polymer as this polymer appears to exhibit poor thermal conductivity. Unlike continuous processes, which achieve a dynamic process equilibrium thereby maintaining control of reaction temperatures and residence times, batch, semi-batch and serial batch processes are continually in a state of disequilibrium, posing chronic control challenges with every process cycle and acute problems of reactor fouling. Other variables, including catalysts, are optimizers; although catalytic cracking and reforming offers advantages of polymer breakdown at lower temperatures and higher rate with added control on product quality, catalytic cracking poses challenges including process complexity, deposition of residues hindering activity, poisoning of catalysts, high capital and operating cost of catalyst reactors, and cost of disposal of spent catalyst.
Hydrogenation is a basic step in petroleum refining and petrochemical production that has been applied to secondary processing of oil resulting from thermal cracking processes. This secondary method, often coupled with distillation, is employed in the production of petroleum-based fuels and process cuts where hydrogen saturation of olefins and removal of heteroatoms is required. Hydrogenation is capital intensive, and can have high operating cost attributed to high pressure operation, cost of hydrogen, cost of removing waste heat, and other factors. The term “heteroatom” is understood to mean any atom that is not carbon or hydrogen, and has been applied to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure or replaced hydrogen or alkyl groups bonded to the backbone of the molecular structure. Typical heteroatoms are nitrogen, oxygen, sulfur, phosphorus, chlorine, bromine, fluorine and iodine. Hydrogenation is a secondary process deployed in petroleum refining and petrochemical production.
Prior art systems and processes have not achieved wide acceptance or success involving pyrolytic decomposition of polymers and this has been attributed to high operating costs, inability to consistently process contaminated waste streams and waste streams of varying composition, the prohibitively high cost or lack of market availability of uncontaminated raw material streams, inability to reliably and efficiently control temperature and pressure process conditions, inability to consistently supply adequate quantities of in-specification raw material to plants requiring high volumes of material to sustain operations, inability to control system fouling by char, terephthalic acid, benzoic acid, minerals, metals and the like, attempts to produce fuel having comparatively narrow ranges of market-driven specifications from widely varying raw material compositions, inability to control heteroatom content of product oil thus limiting market acceptance of the products, inability to consistently and effectively manage safety issues attributed to worker exposure to hazardous vapors and solids in every batch reactor cycle, and generation of hazardous waste including but not limited to char, waste water and off-specification hydrocarbonaceous liquids.
More specifically, prior art involving batch or semi-batch processes must overcome challenges of thermal inefficiency to promote conversion. Given that polymer waste has poor thermal conductivity, most batch reactor systems rely on some configuration of mixing elements within the reactor or complex arrays of raw material-containing cartridges placed into the batch reactor or concentric tubular devices containing raw material subjected to thermal energy or tubular heat transfer geometries deployed within the body of the batch reactor and the like, with the intent to increase raw material surface area, thereby increasing surface exposure to thermal energy which is otherwise poorly conveyed through material having poor thermal conductivity. The large number of batch reactor configurations that have sought patent protection is consistent with a broad-spectrum series of attempts to solve the heat transfer and process control challenges inherent to batch reactor systems. Complex mechanical and/or geometric solutions to the limitations are inherent to batch reactors.
Additionally, most if not all batch reactors, whether singly or in series, must be charged with hydrocarbonaceous raw materials, purged of atmospheric air containing oxygen, heated to the desired temperature when product vapors are extracted, then cooled to a temperature below flash point of the residual solids to facilitate their removal. The repeated thermal cycles experienced by these systems have poor thermal efficiency resulting in overconsumption of energy to complete the polymer conversion.
In an embodiment of the batch process, U.S. Pat. No. 8,192,587 to Garrison et al provides limited means of process control. In a batch reactor, all of the chemistries in the batch reactor described by Garrison are decomposed at successive times in the same three-dimensional space. Without the addition of the complex geometric means in Garrison to increase surface area available for heat transfer in a batch reactor by circulating heat transfer fluid through a sealed heating system, temperature control over the internal cross section of the reactor is poor because of poor thermal conductivity and varying material densities in the raw material charge. Such material densities change as conversions occur and mass is removed from the reactor via discharge of vapor. Moreover, poor thermal conductivity of polymer raw materials in a batch reactor, such as in Garrison, even with internal heat transfer fluids deployed results in varying degrees of raw material thermal transfer capacity across the complex cross section of the batch reactor. Additional complexity arises from change in thermal conductivity of the raw material as its composition changes as it decomposes. Further inefficiency in a batch reactor system such as in Garrison results from deposition of heavy oligomer, polynuclear aromatic hydrocarbons, asphaltines and/or char upon the surface of the internal heat transfer system and upon the surface of the reactor body itself, thereby offering an incomplete thermal conductivity solution to promotion of efficient heat transfer. As waste polymer decomposes in place in an unstirred reactor as described by Garrison, deposition of char on the internal surface of the reactor for much of the reactor cycle promotes formation and adsorption of aromatic and polynuclear aromatic hydrocarbons onto the surface of the char. Unless those aromatic and polynuclear aromatic hydrocarbons are removed from the char or unless this adsorption is prevented, disposal of the char created by the batch process can be rendered prohibitively expensive if it is characterized as a hazardous waste. As with all batch reactors, at the end of each process cycle, the char must be removed.
U.S. Pat. Nos. 5,389,961 5,740,384 to Cha et al describe a continuous, two-step thermal process for co-recycling scrap tires and oils. This prior art processes scrap tire with relatively large amounts of used motor oil, cylinder oil, vacuum tower bottoms and the like Cha describes a dual-reactor system operated in series whereby a transfer point between the two reactors is required to discharge un-reacted material from the first inclined reactor to the second horizontal reactor. This transfer point results in operational challenges as a result of fouling. Cha describes a cross-sectional shape of the dual-reactor system which provides for an open headspace through which un-reacted tire components, including steel fibers, could move, said open headspace posing a challenge to efficient transport of raw material up the incline of the first reactor. Cha describes operating the inclined reactor at increasing temperature, and operating the horizontal a higher temperature to drive off volatile hydrocarbons from the char.
U.S. Pat. No. 5,836,524 to Wang describes a process that processes solid polymer waste and used lubricating oils or recycled heavy oil in a single continuous step at relatively low temperatures. This prior art employs a continuous process inclined screw having no means for control in rate of temperature ramp and control of residence time. Wang recognizes that process yield is a function of temperature.
U.S. Pat. No. 6,172,275 to Tadauchi et al describes a pyrolysis method and apparatus for decomposing waste plastic which may contain organic chlorine. Tadauchi teaches the use of heating zones for decomposition of plasticizers and for dechlorination of halogenated polymer including polyvinyl chloride (PVC), by which the plasticizers can be decomposed to oil and hydrochloric acid, which can evolve from PVC. Both the oil and the hydrochloric acid are separately recovered. Tadauchi further describes condensation and isolation of wax from lighter molecules which may contain organic chlorine compounds, and further pyrolyzing of that wax fraction to light oil. Tadauchi teaches plasticizer decomposition and hydrochloric acid evolution, noting only that additional decomposition occurs at temperatures at or above 450° C. (842° F.) to produce a pyrolysis product, which can be light oil dominated by 4-15 carbon atoms. Tadauchi teaches that the material remaining after decomposition of plasticizers and recovery of hydrochloric acid are subjected to a pyrolysis process generally exceeding 450° C. (842° F.). Tadauchi describes a vacuum to remove hydrochloric acid from the plastic and increasing reactor pressure coincident with pyrolysis to shift molecular distribution toward lighter molecules having 4-15 carbon numbers.
U.S. Pat. No. 7,344,622 to Grispin describes what is called a continuous process wherein control upon the composition of liquids resulting from the thermal decomposition of polymer waste is achieved by maintaining a slow heating rate in the substantial absence of oxygen, creating a char bed having a thermal gradient. Grispin suggests that the nature of the char bed, reactor size, the amount of raw material charge, heating rate and the substantial exclusion of oxygen are simultaneously related to the composition of the product. The process described by Grispin operates by achieving a controlled single heat ramp for an optimal time period in a reactor targeting a relationship between reactor volume and reactor charge, to impact the composition of the oil formed thereby. Grispin's teaching is for a process for the production of aromatic fractions having 6-12 carbon numbers.
U.S. Pat. No. 7,893,307 to Smith describes a process whereby “hydrocarbon-formable materials, such as plastics and other waste or other recycled materials” are melted in a “viscous shear apparatus” such as an extruder and introduced into a device described as a “ribbonchannel” reactor wherein a cylindrical ribbon of melted plastic having a thin cross-sectional area is advanced and wherein pyrolytic decomposition of the plastic occurs. The intent of this design is to maximize surface area available to heating by exposing the thin body of melted material to a skin temperature far above that which is necessary to promote polymer decomposition, thus imparting a high thermal gradient to the material in the reactor. The temperature of melt exiting the viscous shear apparatus and entering the ribbonchannel reactor is claimed to range from about 238° C. (460° F.) to about 315° C. (600° F.). In the Smith process, effective dechlorination, if any, occurs between about 300° C. (572° F.) to about 365° C. (690° F.). Smith further discloses that residual material is discharged from the ribbonchannel reactor in a temperature range from about 524° C. (975° F.) to about 538° C. (1000° F.). To achieve decomposition in the ribbonchannel reactor, the skin temperature/heating element temperature of the ribbon channel reactor ranges from about 760° C. (1400° F.) to about 1315° C. (2400° F.) in an effort to efficiently heat the thin cross section of material filling the ribbon channel by maintaining a high temperature differential between the reactor skin and internal reactor temperature. This heating results in internal ribbonchannel reactor temperatures increasing from 338° C. (640° F.)-368° C. (694° F.) up to 393° C. (740° F.)-524° C. (975° F.) where pyrolytic decomposition is achieved, optionally in the presence of a melt-phase catalyst. Char material, dirt, and small pieces of metal are discharged at the end of the process about 524° C. (975° F.) to about 538° C. (1000° F.). Smith's teaching is to a process throughput of 3,000 to 10,000 pounds per hour, and focuses on the geometry of the ribbonchannel reactor to optimize rapid heat transfer. The extruder and ribbonchannel reactor cannot accept particles larger than the clearance between the extruder screw and barrel, or the effective distance between the inner diameter of the outer heated cylinder and the outer diameter of the inner heated cylinder, whichever is smaller. In the exemplary case of rubber, Smith articulated far smaller particle sizes including crumb. Smith focuses only on providing a solution to effective heat transfer.